Many materials such as plastics, elastomers, lubricants, cosmetics and petroleum products (such as hydraulic fluids, oils, fuels and oil/fuel additives for automotive and aviation applications) are prone to degradation upon prolonged exposure to light, heat, oxygen, ozone, repetitive mechanical actions and the like. Accordingly, compounds and compositions demonstrating antidegradant efficacy are well known in the art. For example, U.S. Pat. No. 8,987,515 discloses an aromatic polyamine useful in inhibiting oxidative degradation particularly in lubricant compositions. U.S. Patent Application Publication number 2014/0316163 discloses antioxidant macromolecules with purported improved solubility in many commercially available oils and lubricants.
Antidegradants useful in the manufacture of articles formed from elastomers, plastics and the like require a very specific combination of qualities that can be difficult to achieve. While the antidegradants must obviously have commercially acceptable efficacy, they must also exhibit that efficacy over prolonged periods of time associated with use of the article, particularly at exposed surfaces of the article where degradation from environmental factors such as light, oxygen and ozone primarily occurs. Just as important to the protection of surface exposed components, efficacy in protecting imbedded components of composite materials from the effects of oxidative aging and repetitive mechanical action are critically important. The antidegradants must achieve these results while not negatively impacting other additives' efficacy or desirable characteristics in the final article. Further, antidegradants which provide or improve the mechanical fatigue life after an article has been in service, aged oxidatively or by exposure to ozone are highly valued since these will inherently improve the useful mechanical service life of article. Consequently, elastomeric articles which undergo repeated mechanical flexure, extension, or compression during service would greatly benefit from such a discovery.
Articles formed from general purpose elastomers such as natural rubber, in particular tires, are especially prone to degradation from both oxygen and ozone. As discussed in U.S. Pat. No. 2,905,654, the effect on rubber from degradation by oxygen is different from the effect from degradation from ozone; however, both effects can be detrimental to tire performance, appearance and life expectancy. Fatigue and crack propagation are also issues of specific concern, in particular for steel belt edge areas and tire sidewalls which are subject to significant stresses and stretching forces while flexed whether inflated, partially inflated and throughout the service life of the tire. U.S. Pat. No. 8,833,417 describes an antioxidant system that purportedly increases long-term resistance to fatigue and crack propagation over the known antioxidants discussed immediately below.
Materials with antidegradant efficacy are well known in the art for use in tire applications and are commercially available. For example, N,N′-disubstituted-paraphenylenediamines such as those sold by Eastman Chemical Company under the trademark Santoflex® are generally favored by many tire manufacturers for this purpose. EP Pat. Appln. Publn. No. EP 3 147 321 A1 discloses rubber compositions, tires, amine compounds, and anti-aging agents, and in particular, a rubber composition that is said to be suitable for use in tread rubber or sidewall rubber of a tire. As governmental regulation, market needs and customer expectations push the rubber industry toward lighter weight tires to enhance fuel efficiency and conserve natural resource feedstocks, a continuing need nonetheless exists for improved antidegradants, and methods of making them, that exhibit (i) multiple efficacies against fatigue, crack propagation and the various mechanisms of degradation; (ii) increased efficacy, especially at lower concentrations and (iii) longer efficacy periods when compared to current commercial materials.